INHIBITION OF LUNG CALCIUM-INDEPENDENT PHOSPHOLIPASE A(2) BY SURFACTANT PROTEIN-A
INHIBITION OF LUNG CALCIUM-INDEPENDENT PHOSPHOLIPASE A(2) BY SURFACTANT PROTEIN-A
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DOI：
10.1152/ajplung.1994.267.3.l335
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发表时间：
1994-09-01
影响因子：
--
通讯作者：
CHANDER, A
中科院分区：
文献类型：
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作者：
FISHER, AB;DODIA, C;CHANDER, A
观察肺表面活性蛋白A（SP-A）对肺磷脂酶A2（PLA 2）活性的影响。从肺灌洗获得的牛表面活性剂中纯化SP-A。使用放射性标记的1，2-二棕榈酰磷脂酰胆碱（DPPC）在表面活性剂样单层脂质体中用无钙酸性（pH 4）或10 mM Ca 2+碱性（pH 8.5）缓冲液测定PLA（2）。SP-A显著抑制大鼠肺匀浆或分离板层体的钙非依赖性酸性PLA（2），但对钙依赖性碱性酶无影响。0.25 μ g SP-A/μ g板层体蛋白抑制50%的板层体PLA（2）。当1-棕榈酰，2-油酰PC（POPC）为底物时，观察到SP-A的类似抑制作用。结合实验表明，I-125标记的SP-A与DPPC结合，但不与POPC结合，表明除去底物不是SP-A抑制酶的机制。SP-A的化学还原或烷基化可消除其对PLA（2）活性的抑制作用。在分离的板层体或表面活性剂的内源性SP-A的失活增加的Ca 2 +-非依赖性的PLA（2）的活性在这些馏分。脂质体中SP-A的存在刺激了原代培养的肺颗粒细胞对DPPC的摄取，但显著抑制了DPPC的降解。这些结果表明，非钙依赖性酸性PLA（2）在内化的表面活性剂磷脂的代谢中起作用，SP-A可以调节这种酶的活性。
The effect of lung surfactant protein A (SP-A) on lung phospholipase A(2) (PLA(2)) activity was investigated. SP-A was purified from bovine surfactant obtained by lung lavage. PLA(2) was assayed using radiolabeled 1,2-dipalmitoyl phosphatidylcholine (DPPC) in surfactant-like unilamellar liposomes with Ca2+-free acidic (pH 4) or 10 mM Ca2+, alkaline (pH 8.5) buffer. SP-A significantly inhibited Ca2+-independent acidic PLA(2) of rat lung homogenate or isolated lamellar bodies but had no effect on the Ca2+-dependent alkaline enzyme. Lamellar body PLA(2) was inhibited by 50% with 0.25 mu g SP-A/mu g lamellar body protein. Similar inhibition by SP-A was observed when 1-palmitoyl,2-oleoyl PC (POPC) was the substrate. Binding assay showed binding of I-125-labeled SP-A to DPPC but not to POPC, indicating that removal of substrate was not the mechanism for inhibition of the enzyme by SP-A. Chemical reduction or alkylation of SP-A abolished its inhibitory effect on PLA(2) activity. Inactivation of endogenous SP-A in isolated lamellar bodies or surfactant increased Ca2+-independent PLA(2) activity in these fractions. The presence of SP-A in liposomes stimulated the uptake of DPPC by isolated granular pneumocytes in primary culture but significantly inhibited its degradation. These results indicate that the Ca2+-independent acidic PLA(2) has a role in the metabolism of internalized surfactant phospholipid and that SP-A can modulate the activity of this enzyme.